Silicon photonic waveguide biosensor configurations

ABSTRACT

Methods and devices relating to sensors and sensor blocks for use in detecting and monitoring molecular interactions. A silicon waveguide sensing element is provided along with a layer of silicon. A silicon oxide layer is also provided between the waveguide element and the layer of silicon. The sensing element is adjacent to an aqueous solution in which the molecular interactions are occurring. A light beam travelling in the silicon waveguide creates an evanescent optical field on the surface of the sensing element adjacent to the boundary between the sensing element and the aqueous medium. Molecular interactions occurring on this surface affect the intensity or the phase of the light beam travelling through the waveguide by changing the effective refractive index of the medium. By measuring the effect on the intensity, phase, or speed of the light beam, the molecular interactions can be detected and monitored in real time. Various configurations using this sensor technology is also disclosed.

FIELD OF THE INVENTION

The present invention relates to sensor technology. More specifically,the present invention relates to sensors for detecting and quantifyingmolecular interactions by determining how much of an effect thesemolecular interactions have on characteristics of light passing througha waveguide adjacent an aqueous medium where these interactions areoccurring.

BACKGROUND TO THE INVENTION

The recent increase in interest in and funding for the biochemical andpharmaceutical fields has created a need for more sensitive sensors thatcan detect and quantify molecular interactions. The detection of thesemolecular interactions determine whether chemical and biologicalprocesses are at work and, as such, are key to finding new and moreeffective pharmaceuticals.

Unfortunately, current biosensor technology suffers from a fragility andscarcity of the equipment. Current sensor technology, such as surfaceplasmon resonance (SPR), is quite well-known but the equipment requiresdelicate handling by technicians. Furthermore, such current technologieshave sensitivities that are less then desirable. With SPR, thesensitivity of the equipment is limited by the short propagation lengthof the plasmon.

There is therefore a need for methods and devices that mitigate if notovercome the shortcomings of the prior art.

Specifically, there is a need for techniques and devices which are easyto implement, robust, and whose sensitivity is not determined by theshort propagation lengths of plasmons.

SUMMARY OF THE INVENTION

The present invention provides methods and devices relating to sensorsand sensor blocks for use in detecting and monitoring molecularinteractions. A silicon waveguide sensing element is provided along witha layer of siliconA silicon oxide layer is also provided between thewaveguide element and the layer of silicon. The sensing element isadjacent to an aqueous solution in which the molecular interactions areoccurring. A light beam travelling in the silicon waveguide creates anevanescent optical field on the surface of the sensing element adjacentto the boundary between the sensing element and the aqueous medium.

Molecular interactions occurring on this surface affect the intensity orthe phase of the light beam travelling through the waveguide by changingthe effective refractive index of the medium. By measuring the effect onthe intensity, phase, or speed of the light beam, the molecularinteractions can be detected and monitored in real time. Variousconfigurations in which the sensor can be used, such as in a ringresonator or a Mach-Zehnder interferometer, are also illustrated.

In one aspect, the present invention provides a sensor for use indetecting molecules in a liquid or gas medium, the sensor comprising:

-   -   a substrate layer,    -   a light waveguide sensor element adjacent said medium    -   a lower cladding layer between said sensor element and said        substrate layer    -   wherein    -   molecular interactions at the waveguide surface affect at least        one characteristic of light travelling through said waveguide        sensor element.

In another aspect, the present invention provides a method for detectingmolecular interactions in a medium using a sensor having a lightwaveguide sensor element adjacent said aqueous medium, the methodcomprising:

-   -   a) determining characteristics of light prior to said light        entering said sensor element    -   b) passing light through said sensor element    -   c) determining characteristics of light after it has exited said        sensor element    -   d) comparing results of steps a) and c) to determine if changes        in characteristics of said light occurred    -   e) in the event said changes in characteristics occurred,        measuring said changes    -   wherein a presence of molecular interactions in said medium        affect at least one characteristic of said light.

In a further aspect, the present invention provides an optical sensorblock for use in detecting molecules in a liquid or gas medium, thesensor block comprising:

-   -   a group of sensors comprising at least two sensor elements        wherein each sensor element comprises        -   a substrate layer        -   a light waveguide sensor adjacent said medium        -   a lower cladding layer between said waveguide sensor and            said substrate layer        -   wherein        -   molecular interactions at the waveguide sensor surface            affect at least one characteristic of light travelling            through said waveguide sensor        -   light travelling through said waveguide sensor is for            eventual reception by an optical detector.

Another aspect of the invention provides an optical sensor block for usein detecting molecules in a liquid or gas medium, the sensor blockcomprising:

-   -   a Mach-Zehnder interferometer having a first and a second arm,        said first arm being a sensor arm having an optical sensor        element, said optical sensor element comprising:        -   a substrate layer        -   a light waveguide sensor adjacent said medium        -   a lower cladding layer between said waveguide sensor and            said substrate layer        -   wherein    -   molecular interactions at the waveguide sensor surface affect at        least one characteristic of light travelling through said        waveguide sensor    -   light travelling through said waveguide sensor is for eventual        reception by an optical detector.

A further aspect of the invention provides a sensor for use in detectingmolecules in a liquid or gas medium, the sensor comprising:

-   -   a substrate layer,    -   a light waveguide sensor element adjacent said medium    -   a lower cladding layer between said sensor element and said        substrate layer    -   wherein    -   molecular interactions at the waveguide surface affect at least        one characteristic of light travelling through said waveguide        sensor element    -   and wherein said sensor element is configured as a ring        resonator.

In another aspect, the present invention provides a sensor for use indetecting molecules in a liquid or gas medium, the sensor comprising:

-   -   a substrate layer,    -   a light waveguide sensor element adjacent said medium    -   a lower cladding layer between said sensor element and said        substrate layer    -   wherein    -   molecular interactions at the waveguide surface affect at least        one characteristic of light travelling through said waveguide        sensor element    -   and wherein said sensor element is configured as one arm of a        Mach-Zehnder interferometer.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be described with reference to the accompanyingdrawings, wherein:

FIG. 1 is an isometric view of a sensor according to one aspect of theinvention;

FIG. 2 is a front cut-away view of the sensor of FIG. 1 illustrating thecore of the waveguide;

FIG. 3 is a side cut-away view of the sensor of FIG. 1 illustrating thedirection of propagation of light travelling in the waveguide and theevanescent optical field produced by such light;

FIG. 4 illustrates the positioning of a molecular layer on a surface ofthe sensor of FIG. 1;

FIG. 5 is a side cut-away view of the sensor of FIG. 1 with a sensorwindow;

FIG. 6A illustrates a configuration of a sensor in which the silicondioxide layer is provided as pillars supporting the waveguide;

FIG. 6B illustrates a top-down view of a configuration of the sensorwhich can be used as a ring resonator;

FIG. 7 illustrates a sensor configuration in which the sensor can beused as a microdisk resonator;

FIG. 8 illustrates a sensor configuration with dual arms;

FIG. 9 shows a configuration with a spiral arm;

FIG. 10 illustrates a sensor configuration using a coupler with fourwaveguide arms;

FIG. 11 shows a ring configuration for the sensor;

FIG. 12 a-FIG. 12 d illustrate four closer views of the ringconfiguration of FIG. 11;

FIG. 13 shows a configuration with dual ring sensors;

FIG. 14 illustrates multiple ring sensor configurations;

FIG. 15 illustrates the sensor configuration of FIG. 14 terminating witha loop mirror;

FIG. 16 illustrates a Mach-Zehnder configuration for the sensor;

FIG. 17 illustrates the configuration of FIG. 16 with the addition of amodulator;

FIG. 18 illustrates a Mach-Zehnder configuration for the sensorterminating with a photodetector array;

FIG. 19 schematically details multiple Mach-Zehnder configured sensors;

FIG. 20A-20B illustrates two different Mach-Zehnder configurationsensors;

FIG. 21A-FIG. 21C illustrate three sensors which use an unbalancedMach-Zehnder configuration with a reduced temperature sensitivity;

FIG. 22 shows a Mach-Zehnder interferometer sensor comprising awaveguide section with a large group index for sensitivity enhancement;

FIG. 23 illustrates a 1×N addressable sensor array;

FIG. 24 illustrates a sensor array which use vertically coupled inputand output beams;

FIG. 25 illustrates a sensor array which uses twomultiplexer/demultiplexers.

DETAILED DESCRIPTION

Referring to FIG. 1, a sensor 10 according to one aspect of theinvention is illustrated. The sensor 10 has an optical waveguide 20 (asensor element) on top of a silicon dioxide layer 30. The silicondioxide layer 20 (a lower cladding layer) is sandwiched between thewaveguide 20 and a silicon substrate 40.

Referring to FIG. 2, an end cut-away view of the sensor 10 isillustrated. In use, from FIG. 2, a solution 50 (which may be waterbased) is adjacent the waveguide 20. The 50 contains the chemical orbiochemical materials whose interactions are to be monitored ordetected.

The sensor detects molecular interactions (or the presence of specificmolecules) by having light passed through the sensor. The sensor detectsthe binding of specific, target molecules to receptor molecules on thewaveguide surface. By detecting this binding, the presence of the targetmolecules is determined. The receptor molecules are previously attached(perhaps as a layer) to the waveguide surface. As an example, anantibody can be fixed to the sensor surface (the waveguide surface) tofunctionalize the antibody for detecting the presence of thecorresponding antigen.

Referring to FIG. 3, a side-cutaway view of the sensor is illustrated.The sensor 20 operates by detecting the effect of target moleculesbinding to the waveguide surface on the characteristics of light as thelight travels through the waveguide.

As is well-known in the art, especially to those well-versed in SPRtechnology, target molecules are detected when they bind to the surface50A of the sensor. Light travelling in the waveguide 20 (in thedirection 60 of propagation) produces an evanescent optical field 70 onthe surface of the waveguide 20. The molecular interactions occurringnear or at the surface 50A affect the refractive index of the liquidsolution, thereby slowing down or delaying the light travelling throughthe waveguide. This effectively changes the speed and othercharacteristics of the light in the waveguide. Characteristics such asthe intensity and the phase of the light are affected by the extent andnumber of molecular interactions on the surface of the waveguide.

Molecular interactions, such as the adsorption of molecules onto thesensor surface affect the speed of light as well as the attenuation ofthe light. The attenuation of the light also depends on the absorptioncross section at the optical wavelength of the light travelling in thewaveguide. As noted above, a phase change in the light in the waveguidemay also be induced due to the adsorption of a molecular layer on thesurface of the waveguide.

The changes in the characteristic of the light in the waveguide can bedetected and measured by the use of well-known devices and techniques.Such devices as Mach-Zehnder interferometers and resonators may be usedto measure these changes in characteristic. These same devices may beused to determine the initial characteristics of the light prior totheir entering the sensor. Once the initial characteristics of the lightare determined, these can be compared to the characteristics of thelight after the light has passed through the sensor. The differencesbetween these two sets of characteristics (such as speed of light,phase, etc.) would indicate the presence and number of molecularinteractions detected.

Referring to FIG. 4, another cross-sectional view of the sensor isillustrated. As can be seen, the molecular layer 50B forms between thesurface of the waveguide and the aqueous medium. Experiments have shownthat sensor response increases with active sensor length and that sensorresponse increases with mode intensity at the perturbation location(i.e. the target molecule layer). The presence and number of targetmolecules can therefore be determined by sampling the characteristics(e.g. attenuation, phase, etc.) of the light travelling in thewaveguide.

Experiments have shown that best results have been observed whensilicon-on-insulator waveguides were used. Silicon photonic wirewaveguides have been found to produce useful as the sensor elements inthe sensor. For better results, a sensor window may be used to isolatethe area where the waveguide core is exposed to the target molecules, toenable a comparison of the light travelling through the sensor waveguidewith light travelling in an unexposed reference waveguide. Referring toFIG. 5, such a sensor window is illustrated. An isolation layer 80isolates the evanescent optical field 70 from the aqueous medium 50 andthe molecular interactions. A sensor window 90, an area in which theisolation layer is not present, exposes the evanescent optical field 70to the medium 50 and thereby to the changed refractive index due totarget-receptor molecule interactions. It should be noted that theisolation layer may be fabricated using well-known photosensitivepolymer coatings normally used in the fabrication of semiconductordevices.

It should be noted that various configurations of the above noted sensorare possible. Referring to FIGS. 6A, 6B and 7, two differentconfigurations are illustrated. FIGS. 6A and 6B illustrate a bridgeconfiguration with the waveguide core being supported by pillars 80 ofsilicon oxide. This configuration allows the aqueous medium to surroundthe waveguide and thereby increase the surface area on which themolecular interactions can occur. Such a configuration can also be usedto create a ring resonator as in FIG. 6B. In FIG. 7, a microdiskresonator can be configured using a single silicon oxide pillar 80 tosupport a microdisk waveguide sensor.

Experiments have also shown that better results have been achieved whenthe waveguides were thin as well as having a high contrast in terms ofrefractive index. Thus, better results were found when the contrastbetween the effective refractive index (N_(eff)) and the refractiveindex of the cladding was at a maximum. Also, it has been found thatbetter results were achieved when the polarization of the lighttravelling in the waveguide was perpendicular to the active surface (theso-called TM mode). One material which produced acceptable results (thinwaveguide, high index contrast, and TM mode) were silicon photonic wirewaveguides. However, other materials may also provide equally acceptableresults.

It should also be noted that the presence of a thin layer (i.e. thelayer must be thinner than the extent of the evanescent field above thewaveguide) of silicon dioxide between the waveguide and the mediumcontaining the molecular interactions does not significantly degrade theperformance (sensitivity) of the sensor. As such, a layer of silicondioxide (i.e. glass) may be deposited on the waveguide.

Based on the above, silicon or other established glass bio-chipchemistries may be used in the production of the above noted sensorelements.

The above sensor technology may be used in a number of configurations.These configurations may enhance the results obtained by the sensor byincreasing the area exposed to the material being sensed or theconfigurations may make it easier to interrogate the sensor.

The sensors may be arranged as a sensor block with multiple sensors.FIGS. 8-25 illustrate various embodiments of such a sensor block.

Referring to FIG. 8, the sensor block 500 has a single input 510 and asingle output 520. Between these is a reference arm 530 and a sensorwindow 540. The reference arm 530 and the sensor window 540 areconstructed by having the light waveguide element 550 configured as asingle weaving pattern with each trace of the pattern being parallel tothe other traces to result in a grid-like pattern of parallel lines,preferably as closely packed parallel lines. In weaving terminology, thepattern traced by the waveguide element would be the same as that tracedby a weft yarn (or the “fill yarn” or “woof yarn”) in plain weaving. Ascan be seen from the figure, the single input 510 is split into twopaths—one of which turns into the sensor window while the other turnsinto the reference arm. The outputs of the sensor window and of thereference arm then combine into the single output 520. The lightwaveguide sections in the sensor window are exposed to the materialbeing sensed while the sections in the reference arm are not exposed tothe material.

Referring to FIG. 9, the light waveguide sensor may be configured as asensor block 600 with a sensor element arranged as a spiral 610. As canbe seen from the figure, this sensor block arrangement has the samesingle input and output. At the end of the spiral may be placed amirrored Bragg grating loop or similar device. The spiral section 610 isexposed to the material being sensed. The spiral section may beconfigured as a unifilar mirrored spiral.

The spiral section may also be configured as a bifilar spiral. Sucharrangement obviates the need for a mirror and provides physicallyseparated input and output waveguides.

Referring to FIG. 10, the sensitivity of the sensor can be amplified byusing a resonator effect. A linear two-mirror resonator 620 isillustrated in FIG. 10. A coupler 630 couples four waveguides—an inputwaveguide 640, an output waveguide 650, a sensing window waveguide 660,and an optional shifter waveguide 670. As can be seen from the figure,the sensing window waveguide terminates at a mirror 675, for example aBragg reflector, a metallic mirror, or a loop mirror. The optional phasecompensator/shifter waveguide 670 also terminates in a similarmirror/reflector. The signal enters through the input 640 and is sensedthrough the sensing window 680 and is reflected back by themirror/reflector 675. The signal exits via output 650.

Referring to FIGS. 11 and 12, the sensor block 703 may, again, have asingle input 710 and a single output 720. The sensor element 730 in thesensor window 740 may be configured as a ring resonator with a multimodeinterference (MMI) coupler 750. One preferred configuration (withmeasurements) of the MMI coupler is illustrated in FIG. 12 b). Theappearances of the ring resonator and of the coupler, as implemented insilicon, are shown in FIGS. 12 c) and d). In this configuration, thering resonator structure would be exposed to the material being sensedas the structure would be within the sensor window.

Referring to FIG. 13, the ring resonator structure may be used in avariety of configurations. In FIG. 13, two ring resonators are placedside by side such that the output of resonator L1 becomes the input toresonator L2. In this configuration, the L1 resonator is inside a sensorwindow and, as such, is exposed to the material being sensed. The L2resonator may be used as a reference to cancel out signal variations dueto temperature. As is known, a single ring resonator will have aresonance wavelength that shifts with temperature asdλ/dT˜(L/m)(dN_(eff)/dT), where m is the ring order. However, theseparation in wavelength resonances for two ring resonators of nearlythe same ring path length will be significantlysmaller—d(λ₁−λ₂)/dT˜((L1−L2)/m)(dN_(eff))/dT). Opening a sensor windowover one ring and covering the other ring to act as a reference andusing the difference in resonance wavelength as the transduction signalmay cancel out the transduction signal variations due to temperature.

Referring to FIG. 14, ring resonators may be used in otherconfigurations. In FIG. 14, the sensor block 800 has a single input 810and a single output 820 with ring resonators 830, 840, 850. Each ringresonator may be wavelength addressable such that each ring resonatoronly responds to a single wavelength or a specific range of wavelengths.Each ring resonator may be configured so that it has a specificresonance wavelength and each resonator can be individually monitored bymeasuring the wavelength shift of its resonance. Addressing and signalmonitoring for each resonator may be done by sending only one lightinput at a time with the light having a specific wavelength to address asingle resonator. The output 820 may then be measured by a detector 860which may or may not be part of the sensor block. The detector 860 maybe a photodetector if only one wavelength of light at a time is inputtedinto the sensor block. Alternatively, the detector 860 may be aspectrometer if a broad spectrum of light is inputted—the positions ofall the resonances may be monitored if the spectrometer is used. Ofcourse, each of the ring resonators in this configuration is in a sensorwindow and, as such, each resonator is exposed to the material beingsensed.

Referring to FIG. 15, the results from a ring resonator configurationmay be enhanced by passing the same light through the sensor twice. Ascan be seen from FIG. 15, instead of a detector at the end of the sensorblock 900, a loop mirror 910 may be placed at the end of the output ofsensor block. The loop mirror would reflect the output light and thelight would then pass through the relevant ring resonator again. Acirculator 920 would then redirect the returning sensor signal to themeasuring optics and electronics.

Referring to FIG. 16, another configuration of a sensor block 1000 usingthe light waveguide technology explained above is illustrated. In thisconfiguration, a single input is used and the input light is splitbetween two arms of a Mach-Zehnder interferometer. One arm 1020 is usedas a sensor window while the other arm 1030 is used as a reference arm.

The output of each arm is then joined into a single output 1040. As withthe previous configurations, the section of the waveguide in the sensorwindow is exposed to the material being sensed. The other sections ofthe light waveguide are shielded from the material being sensed. In thisconfiguration, if the two arms are designed to have precisely the sameoptical path length and the same average dN_(eff)/DT (with Neff beingthe effective index of the waveguide mode) the output of theMach-Zehnder will be independent of temperature and wavelength. Thesensor block will only respond to the molecular adsorption and indexchanges in the material over the sensor window.

The configuration in FIG. 16 may be adjusted to have an opticalmodulator in the reference arm. Such a configuration is illustrated inFIG. 17. In FIG. 17, the modulator 1050 modulates the effective index ofthe light signal at high frequency. By using lock-in or heterodyningtechniques to measure the modulated component cf the Mach-Zehnder signaloutput, low frequency (e.g. 1/f) noise in the detector and opticalsource may be eliminated.

The ring resonator configuration and the Mach-Zehnder configuration maybe combined into a single sensor block as in FIG. 18. The sensor block1100 has a single input 1110, a reference arm 1120, and a signal arm1130 with a ring resonator 1140 in the sensor window 1150. The output ofboth arms would be received by a 1×N MMI or star coupler 1160. Thisproduces an interference pattern and this can be sampled directly byimaging the output plane of the MMI or sampled with appropriately placedwaveguides 1170 with a photodetector array 1180. This interferencepattern will shift as molecules adsorb on the light waveguide sensor orthe fluid index of the material being sensed changes. As theinterference pattern is the transduction signal, the sensor blockresponse is independent of fluctuations of input light power.

The Mach-Zehnder configuration of the sensor block may be combined withother sensor blocks to arrive at an array of sensor blocks. Referring toFIG. 19, an array of sensor blocks is illustrated. In this array, eachelement of the array has a configuration similar to that illustrated inFIG. X8 in that each array element is a Mach-Zehnder interferometer witha modulator in the reference arm and a sensor window in the sensor arm.The only exception to this is the topmost array element—this arrayelement does not have a sensor window and is used as a reference. Themodulator bias of the topmost array element without the sensor window isadjusted to keep the output of the reference circuit constant. Theoutput of every other sensor block circuit is adjusted with an identicalbias so that drifts due to temperature and environmental effects areeliminated. The signal change is thus only due to molecular adsorptionor fluid index change. It should be noted that while Mach-Zehnderinterferometer configurations are used in FIG. 19, a similarconfiguration used ring resonators is also possible. For such a ringconfiguration, the topmost element is, again, devoid of a sensor window.

The Mach-Zehnder configuration may also be altered to arrive at other,useful sensor blocks. As an example, referring to FIGS. 20A and 20B,these configurations may be useful in reducing the number of fiberattachments. In both configurations, a mirror 1200 is used at the outputof the Mach-Zehnder interferometer. In FIG. 20A, two mirrors areused—one at the end of each arm of the interferometer. In FIG. 20B, onlyone mirror 1200 is used after the combining of the outputs of each arm.In both cases, a circulator 1210 is used to redirect the returningsensor signal to the measuring optics and electronics. For bothconfigurations, as with the other Mach-Zehnder configurations discussedabove, one of the arms has a sensor window 1220.

While conventional Mach-Zehnder interferometer configurations arecontemplated in the configurations noted above, more unconventional MZconfigurations are also useful. As an example, unbalanced Mach-Zehnderinterferometers or ring couplers may be used. Referring to FIGS. 21A,21B, 21C, different configurations are illustrated that use unbalancedMach-Zehnder interferometers. These configurations have a temperatureindependent output by using an appropriate combination of waveguideswith different thermo-optic coefficients (dN_(eff)/dT). In FIG. 21A, aninput signal enters input coupler 1400 and travels to a sensing window1410 by way of a first waveguide 1420. The other arm 1430 from inputcoupler 1400 takes the signal to a second waveguide 1440 and from thereby way of an output arm 1450 to output coupler 1460. Also enteringoutput coupler 1460 is the first waveguide 1420 after passing by thesensor window 1410. The output coupler 1460 sends its output to a signalprocessing unit 1470. The first waveguide 1420, arm 1430, and output arm1450 all have the thermo-optic coefficient of dn₁/dT while secondwaveguide 1440 has a thermo-optic coefficient dn₂/dT.

Referring to FIG. 21B, a different configuration of the unbalancedMach-Zehnder interferometer is illustrated. The couplers 1400, 1460, thesignal processing unit 1470, and sensor window 1410 are in the sameplaces as well as the first waveguide 1420 and the other arm 1430 fromthe input coupler 1400. However, other arm 1430 now continues from theinput coupler 1400 directly to output coupler 1460. The other waveguide1440 travels from a junction point with first waveguide 1420 to thesensing window 1410 and then to another junction point adjacent theoutput coupler 1460. As with the above explanation, the first waveguideand the second waveguide have differing thermo-optic coefficients, withthe first waveguide having a thermo-optic coefficient of dn₂/dT and thesecond waveguide having a thermo-optic coefficient of dn_(i)/dT.

In the configuration of FIG. 21C, three different waveguides are used.The first type of waveguide 1480 exits the input coupler 1400 while atthe same time entering the output coupler 1460. The second type ofwaveguide 1490 couples the segments of the first waveguide between thetwo couplers 1400, 1460. The third waveguide 1495 couples the othersegments of the first waveguide to one another with the sensing windowin the middle of the third waveguide 1495. The second waveguide haslength L1 and a thermo-optic coefficient of dn_(i)/dT while the thirdwaveguide has length L2 and a thermo-optic coefficient of dn₂/dT.

In the configurations of FIGS. 21A-21C, the magnitude and sign of theeffective thermo-optic coefficient of the silicon photonic wirewaveguide can be controlled for example by selecting the waveguide corethickness, the cladding material, and the thickness of the claddingmaterial. As examples, for glass, the dn/dT is approximately 1×10̂−5, fora typical polymer, the dn/dT is approximately on the order of −10⁻⁴, andfor silicon dn/dT is approximately 2×10⁻⁴.

For the sensing window in a Mach-Zehnder interferometer, a photoniccrystal structure, resonator, or grating may be used to increase thegroup index. This would thereby amplify the phase change induced by themolecular adsorption in the sensor window and increase sensitivity. (SeeFIG. 22)

It should be noted that the ring resonators and Mach-Zehnder basedsensors may be used in different configurations possible with thissensor technology. An array of sensors (with each sensor being a ringresonator, Mach Zehnder, or other type of sensor) is also possible andsuch a configuration would allow for the use of a broadband light sourceas the input signal. Referring to FIG. 23, such a configuration isillustrated. A broadband light signal is used as the input and this isreceived by a wavelength demultiplexer or a 1×N splitter 1500. Eachoutput of the demux/splitter 1500 passes through a specific sensor in asensor array 1510. After passing through a sensor in the sensor array,each signal's characteristics are detected by a photodetector in aphotodetector array 1520. The 1×N splitter may be a star coupler.

The configuration in FIG. 23 has photodetectors that are coplanar withthe sensor array. However, this need not be the case. The signal may becoupled out of the surface of each output waveguide using mirrors orgratings or can be coupled out at the end facet of the array.Additionally, the input signal may be vertically coupled into the sensorarray and then either vertically or horizontally coupled out. Aconfiguration with vertical input and output coupling is illustrated inFIG. 24. In this configuration, an input beam array is coupled into thewaveguides at input coupling points 1600. The waveguides 1610 guide theinput signals into sensing windows 1620. Once each signal passes by asensing window, it is then coupled out of the waveguide at outputcoupling point 1630. Multiple output coupling points 1630 may beavailable, with each output coupling point servicing at least onewaveguide. Once the signal is coupled out of the waveguide, itscharacteristics can be detected by a phase detector array (PDA) 1640. Itshould be noted that coupling of signals from waveguide mode to verticalfree space beam mode can be accomplished using etched 45 degree mirrorsor diffraction grating structures.

If a single input signal and a single output signal is desired, aconfiguration as illustrated in FIG. 25 may be used. In FIG. 25, asingle input optical signal 1700 with multiple wavelengths λ₁, λ₂, . . .λ_(n) is received by a wavelength multiplexer 1710. This multiplexersplits the incoming signal into different wavelengths and couples eachsignal with a specific one of a waveguide array 1720, with each one ofthe waveguide array 1720 having a sensor 1730 on the waveguide. Afterthe signal has passed through one of the sensors 1730, it is thenreceived by a wavelength demultiplexer 1740. If there are multiplesignals received by the demultiplexer 1740, these signals are thencombined into a single output signal 1750 with multiple wavelengths λ₁,λ₂, . . . λ_(n).

A person understanding this invention may now conceive of alternativestructures and embodiments or variations of the above all of which areintended to fall within the scope of the invention as defined in theclaims that follow.

1. An optical sensor block for use in detecting molecules in a liquid orgas medium, the sensor block comprising: a group of sensors comprisingat least two sensor elements wherein each sensor element comprises asubstrate layer a light waveguide sensor adjacent said medium a lowercladding layer between said waveguide sensor and said substrate layerwherein molecular interactions at the waveguide sensor surface affect atleast one characteristic of light travelling through said waveguidesensor light travelling through said waveguide sensor is for eventualreception by an optical detector.
 2. An optical sensor block accordingto claim 1 wherein said sensor block has a single optical input and saidsensor block further comprises an optical signal splitting means.
 3. Anoptical sensor block according to claim 1 wherein said sensor block hasa plurality of optical inputs.
 4. An optical sensor block according toclaim 3, wherein said plurality of optical inputs are coupled to saidsensors through an array of vertical waveguide couplers.
 5. An opticalsensor block according to claim 4, wherein at least one of said array ofvertical waveguide couplers is a diffraction grating.
 6. An opticalsensor block according to claim 4 wherein at least one of said array ofvertical waveguide couplers is a 45 degree mirror.
 7. An optical sensorblock according to claim 2 wherein said optical splitting means is anoptical splitter for splitting said single optical input between said atleast two sensor elements in said group.
 8. An optical sensor blockaccording to claim 2 wherein said optical splitting device is an opticaldemultiplexer for demultiplexing said single optical input between saidat least two sensor elements in said group.
 9. An optical sensor blockaccording to claim 1 wherein at least one sensor element in said sensorblock is configured as an optical ring resonator such that for said atleast one sensor element, said light waveguide sensor is configured as aring.
 10. An optical sensor block according to claim 1 wherein at leastone sensor element in said sensor block is configured as a two-mirrorresonator, such that for said at least one sensor element, said lightwaveguide sensor is in a waveguide resonator cavity formed between twomirrors.
 11. A sensor block according to claim 1 wherein at least onesensor element in said sensor block is configured as a spiral such thatfor said at least one sensor element, said light waveguide sensoradjacent said medium is arranged as a spiral.
 12. A sensor blockaccording to claim 1 wherein at least one sensor element in said sensorblock has said light waveguide sensor arranged and configured as asingle weft weaving pattern with each trace of said pattern beingparallel to other traces to result in a grid-like pattern of parallellines adjacent said medium
 13. A sensor block according to claim 1wherein at least one sensor element in said sensor block compriseswaveguide sections with different dn/dT characteristics for reducingsensor temperature sensitivity.
 14. A sensor block according to claim 9wherein the or each of said at least one sensor element is configured asa ring resonator and has a specific resonance wavelength such that aninput beam having said specific wavelength passes through said ringresonator.
 15. An optical sensor block for use in detecting molecules ina liquid or gas medium, the sensor block comprising: a Mach-Zehnderinterferometer having a first and a second arm, said first arm being asensor arm having an optical sensor element, said optical sensor elementcomprising: a substrate layer a light waveguide sensor adjacent saidmedium a lower cladding layer between said waveguide sensor and saidsubstrate layer wherein molecular interactions at the waveguide sensorsurface affect at least one characteristic of light travelling throughsaid waveguide sensor light travelling through said waveguide sensor isfor eventual reception by an optical detector.
 16. An optical sensorblock according to claim 15 wherein said optical sensor element isconfigured as a ring resonator with said light waveguide sensor beingconfigured as a ring.
 17. An optical sensor block according to claim 15wherein said second arm is a reference arm having a modulator. 18-21.(canceled)
 22. A sensor for use in detecting molecules in a liquid orgas medium, the sensor comprising: a substrate layer, a light waveguidesensor element adjacent said medium a lower cladding layer between saidsensor element and said substrate layer wherein molecular interactionsat the waveguide surface affect at least one characteristic of lighttravelling through said waveguide sensor element and wherein said sensorelement is configured as one arm of a Mach-Zehnder interferometer.
 23. Asensor according to claim 22 wherein said sensor element comprises athin, high refractive index contrast waveguide.
 24. A sensor accordingto claim 22 wherein said sensor element comprises a silicon photonicwaveguide.
 25. A sensor according to claim 22 wherein said lowercladding layer comprises a layer of silicon oxide.